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1 // BitlDecoder.h -- the Least Significant Bit of byte is First
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2
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3 #ifndef __BITL_DECODER_H
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4 #define __BITL_DECODER_H
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5
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6 #include "../IStream.h"
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7
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8 namespace NBitl {
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9
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10 const int kNumBigValueBits = 8 * 4;
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11
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12 const int kNumValueBytes = 3;
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13 const int kNumValueBits = 8 * kNumValueBytes;
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14
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15 const UInt32 kMask = (1 << kNumValueBits) - 1;
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16
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17 extern Byte kInvertTable[256];
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18
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19 template<class TInByte>
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20 class CBaseDecoder
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21 {
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22 protected:
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23 int m_BitPos;
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24 UInt32 m_Value;
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25 TInByte m_Stream;
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26 public:
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27 UInt32 NumExtraBytes;
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28 bool Create(UInt32 bufferSize) { return m_Stream.Create(bufferSize); }
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29 void SetStream(ISequentialInStream *inStream) { m_Stream.SetStream(inStream); }
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30 void ReleaseStream() { m_Stream.ReleaseStream(); }
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31 void Init()
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32 {
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33 m_Stream.Init();
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34 m_BitPos = kNumBigValueBits;
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35 m_Value = 0;
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36 NumExtraBytes = 0;
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37 }
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38 UInt64 GetProcessedSize() const
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39 { return m_Stream.GetProcessedSize() - (kNumBigValueBits - m_BitPos) / 8; }
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40 UInt64 GetProcessedBitsSize() const
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41 { return (m_Stream.GetProcessedSize() << 3) - (kNumBigValueBits - m_BitPos); }
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42 int GetBitPosition() const { return (m_BitPos & 7); }
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43
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44 void Normalize()
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45 {
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46 for (;m_BitPos >= 8; m_BitPos -= 8)
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47 {
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48 Byte b = 0;
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49 if (!m_Stream.ReadByte(b))
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50 {
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51 b = 0xFF; // check it
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52 NumExtraBytes++;
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53 }
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54 m_Value = (b << (kNumBigValueBits - m_BitPos)) | m_Value;
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55 }
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56 }
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57
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58 UInt32 ReadBits(int numBits)
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59 {
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60 Normalize();
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61 UInt32 res = m_Value & ((1 << numBits) - 1);
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62 m_BitPos += numBits;
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63 m_Value >>= numBits;
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64 return res;
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65 }
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66
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67 bool ExtraBitsWereRead() const
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68 {
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69 if (NumExtraBytes == 0)
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70 return false;
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71 return ((UInt32)(kNumBigValueBits - m_BitPos) < (NumExtraBytes << 3));
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72 }
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73 };
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74
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75 template<class TInByte>
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76 class CDecoder: public CBaseDecoder<TInByte>
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77 {
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78 UInt32 m_NormalValue;
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79
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80 public:
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81 void Init()
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82 {
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83 CBaseDecoder<TInByte>::Init();
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84 m_NormalValue = 0;
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85 }
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86
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87 void Normalize()
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88 {
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89 for (; this->m_BitPos >= 8; this->m_BitPos -= 8)
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90 {
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91 Byte b = 0;
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92 if (!this->m_Stream.ReadByte(b))
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93 {
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94 b = 0xFF; // check it
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95 this->NumExtraBytes++;
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96 }
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97 m_NormalValue = (b << (kNumBigValueBits - this->m_BitPos)) | m_NormalValue;
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98 this->m_Value = (this->m_Value << 8) | kInvertTable[b];
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99 }
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100 }
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101
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102 UInt32 GetValue(int numBits)
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103 {
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104 Normalize();
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105 return ((this->m_Value >> (8 - this->m_BitPos)) & kMask) >> (kNumValueBits - numBits);
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106 }
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107
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108 void MovePos(int numBits)
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109 {
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110 this->m_BitPos += numBits;
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111 m_NormalValue >>= numBits;
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112 }
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113
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114 UInt32 ReadBits(int numBits)
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115 {
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116 Normalize();
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117 UInt32 res = m_NormalValue & ( (1 << numBits) - 1);
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118 MovePos(numBits);
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119 return res;
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120 }
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121 };
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122
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123 }
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124
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125 #endif
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